Boys outnumber girls when it comes to autism diagnoses, and researchers may have uncovered one reason why.

Boys are four times more likely to be diagnosed with autism than girls, but whether that trend is rooted in biological differences between the genders or the fact that girls might simply hide their symptoms better, hasn’t been clear.

The gender-based difference could be due to factors that increase the risk among boys, or, alternatively, factors that protect girls. Researchers led by Elise Robinson of Harvard Medical School decided to investigate the latter, and determine whether there might be something about being female that protected girls from the the developmental disorder. The team analyzed data from two large samples of twins, one from Sweden and the other from the U.K. They theorized that if something were protecting girls from autism spectrum disorders (ASDs), then families of girls who actually did develop them should have a greater than average risk, and that risk would overwhelm whatever protection they received from their gender. In other words, girls would have a higher threshold for developing ASDs — they would have to be faced with a heavier burden of whatever genetic or environmental risk factors cause ASD in order to actually develop it.

Such family-based risk can be measured by studying levels autistic symptoms in unaffected siblings: in families at high risk of developmental and psychiatric disorders, even unaffected members tend to have mild symptoms, but not enough to qualify for a diagnosis.

“If greater familial [risk] is required to produce autistic impairments in girls, the family members of affected females should on average carry greater risk than the family members of affected males,” the authors write. Because identical twins share the same genetics, they studied fraternal twins only, comparing sets in which only one had an autism spectrum disorder. Nearly 4,000 British twins and just over 6,000 Swedish twins were included in the research, which was published in the Proceedings of the National Academy of Sciences.

The study found that if a girl scored in the top 10% on autistic traits, the odds of her twin scoring in a similarly high range were 37% greater than those for a boy. That meant the girls came from families with significantly greater risk levels. Because the study looked at autistic traits in a sample from the general population, rather than from those who sought treatment, the results do not simply reflect the fact that girls are less likely to be diagnosed, even if they have the condition.

“It is a really interesting and generally well-done study,” says Marjorie Solomon, associate professor of clinical psychiatry at the University of California Davis MIND Institute, who was not associated with the research. She adds, “The differences in gender ratio in ASD have been a source of great curiosity, given their many implications.”

The study was only designed to test the theory that families of girls with ASDs might have higher than risk of the disorders, and was not structured to test for exactly what it is that seems to protect girls. But that knowledge could lead to potentially better treatment options for both genders. Based on earlier research, experts see genes, rather than social or environmental factors, as the most likely explanation for lower risk among girls.

What might some of those genetic factors be? It’s possible that they may involve the social bonding hormones, oxytocin and vasopressin. “The basic thought is that girls have less vasopressin and higher natural oxytocin,” says Solomon, “And oxytocin is a social hormone, so that would be protective.” The lower levels of vasopressin might also be helpful: while this hormone is thought to be involved in social connections—particularly for boys, who tend to have higher levels — in animals it is also linked to aggressive defense of territory and mates.

Or it may involve other metabolic systems that aren’t as obviously connected to social development. Either way, the findings raise interesting questions about how developmental disorders like ASDs are seeded, and open up intriguing new possibilities for treating them. “An understanding of the biology underlying female advantage could greatly aid progress in understanding,” autism and “in identifying prevention factors for ASDs,” the researchers write.

I have heard that Autism is caused by a deficiency of a certain nutrient that is required during pregnancy. There is a great talk about it on YouTube by Dr Joel Wallach, I forgot the name of the video but in it he talks about the different diseases that are brought on by mineral and vitamin deficiencies http://www.seobrisbanehq.com.au/about-us/.

It made a lot of sense, especially when they have all of the animal studies to back it up.

SCPI founder and chief scientist Dr Theresa A Deisher PhD has published a study on AD Prevalence linked to contaminated vaccines since 1979 when CDC secretly changed vaccine manufacturing from animal cell lines to aborted fetal cell lines that have much higher risk of autoimmune disease (Crohn's IBD) and Insertional Mutagenesis that inflames gut blocking immune system from excreting mercury from body resulting in mercury overload in brain and CNS of >75 ppb. CDC refused to notify Congress or public of this change until 2009 (30 years later). CDC and HHS refused to safety test the vaccine manufacturing change. Billy@isp.com

Hopefully as the generations go on in the future, humans will evolve stronger, and able to tolerate Mercury and other deadly poisons. The authorities have always covered up real facts like preserving Vaccines in Mercury-based preservatives. Mercury can slowly send a human-being Mad, and is passed down through sperm/eggs to the next generation. Try to have tooth fillings, without Amalgam (Mercury-based fillings). I had a lot of Amalgam fillings forced on me at the school dentist...Luckily I have felt better since they were removed. Has any-one questioned an increase in Bottle-feeding infants in the last 100 years? Good luck with all the theories :-)

I think you are forgetting one very important aspect, which is that girls with ASD - especially high functioning ASD - may simply be under-diagnosed. Biologically speaking, girls are more likely to have advanced language skills in general in a normal population in comparison to their male peers. In a sense, you may be partially right about a biological "protection" in which girls are more likely to keep their verbal ability. The loss of speech is a major reason parents seek out a diagnosis, but in the event that a child keeps it speech but had difficulties in other Autism related areas the parents may not seek out treatment or the child may be given an alternate diagnosis to describe the other behaviors. Unfortunately, it is very possible, that these undiagnosed girls are still suffering from many of the other hallmarks of the disorder. Because they are undiagnosed, or misdiagnosed, they are not benefiting from getting the proper help.

In the case of high-functioning Autism, many girls are under-diagnosed. It took me 30 years to find someone who diagnosed me appropriately. Obviously, my verbal skills are in tact, but I suffer from many of the other problems that plague people on the spectrum, social problems, sensory problems, etc. Furthermore, in higher functioning individuals, it is important to take a look at how society has separate expectations for males and females. Antisocial boys are allowed to be that way, it is a masculine trait to be independent. Girls are expected from a very young age to be nurturing and social. Many high-functioning girls are pushed by their parents, friends and society at large to be more social. They are forced to keep eye contact and pressured into learning the intricacies of small talk. Because of this, many of them learn to do so just to please the people around them, even to the extent that it may cause them psychological problems because of their inadequacies. Superficially, they appear more "normal" than their male counterparts, even if the still struggle to maintain and keep friendships and jobs. They are more likely to be misdiagnosed mood disorders like anxiety and depression. ADD (especially without hyperactivity), is another common diagnosis as is OCD.

Unfortunately, Autism is often diagnosed based on how a child or person acts outwardly. Girls may outwardly behave differently from their male counterparts but most doctors either can't (because of lack of appropriate language skills in young patients) or don't have in-depth conversations with these types of patients to find out what's going on internally. The perpetuation of the idea that girls are less likely to be on the spectrum is only hurting the Autism community, it causes girls and women to suffer in silence or to be misdiagnosed for secondary symptoms - like anxiety, depression and OCD, that may manifest because of their difficulties in coping with with their sensory and social problems. More, not less attention, need to be focused on finding ways to better diagnose the condition so that more girls are getting the help they need.

The primary reason for autism or any other illness that usually didnt occur in such high level in earlier generations can be single-handedly traced back to age of the mother when she gets pregnant. Average women under the unreasonable, idiotic, influence from militant feminists propaganda have put themselves under extreme stress of trying/proving to 'have it all' without facing the due consequences.

Guess what?, Nature has a simple, effective way of reminding us all who the real boss of this planet is and always will be.

Each and every day, those feminists morons come with yet another way of 'proving' their crackpot concept of 'equality'. No amount of changes to public policy, laws or propaganda can save you sorry assess unless you cure yourselves of the disease of penis-envy that plagues your minds.

No amount of College degrees can guarantee you knowledge leave alone the most important one, wisdom.

People that have children when they are older tend to have more boys. Paternal age has also been a shown to possibly be a factor in Autism. I wonder what the age range of the parents in the study were?

All treatments for autism that show even very slight success are those that introduce very intense social interaction between a caring adult and the infant, but unfortunately always far too late in the developmental process to possibly overcome the damage done by the earlier hidden neglect. Among such families in America many more male infants than female infants are placed on a comfortable shelf and left to develop alone. It’s just that simple. In America you can do anything you want to boys, even systematically screw them over in cribs and schools and gyms, even in the Boy Scouts and churches, and no one will ever say anything (unless there’s money to be made for adults). Give boys a lobby half as powerful as those for women, and just watch the autism discussion “evolve”. (Autism should never be lumped in with those disabilities (much smaller in number) that have similar symptoms but which have clear physiological causes.)

Autism is a consequence of the human brain failing to develop properly. The gross gender differences in diagnosis of childhood autism in the US (which are actually much higher than four-to-one) are due to the same thing that it as always been: infant neglect during the very critical first 1,000 days of life when the brain is developing. Girls in our society receive enormously more attention, from everyone, than do boys – primarily because boys are the only minority group in the US that does not enjoy a powerful lobby. All the efforts, driven by women, to seek causes of social autism elsewhere are simply blame-shifting ploys. All anyone interested in autism has to do is focus on severely understaffed orphanages, such as many in eastern Europe, where it has always been actually possible to study the social interaction provided to infants during those first 1,000 days. This was always the primarily scientific focus prior to the recent huge spike in male autism diagnosis among US white middle class families where parents are pursuing careers and where childbirth has been delayed beyond the optimal period.

Could this be a parenting thing as well? Doesn't lots of hugging, holding, cuddling and touch promote the manufacturing of oxytocin in the bloodstream? I think that we always question what we could do better or differently as parents.

I'd like to see more research into the effects of neurotoxic chemicals in autism. My autistic son is chemically sensitive. He is hypersensitive to neurotoxic fluoride which is widely present in water and thus food. A vaccine triggered his descent into autism (regression), which also contained neurotoxic chemicals. Many autistic people are chemically sensitive. Girls have more redundancy in genetic protection from the effects of toxins due to the extra genes on the leg of the X chromosome (girls are XX and boys XY remember. This could account for the fact that 4 times as many people who are autistic are male. But we all know that they don't find anything they don't want to, so I'm not holding my breath.

It seems to me to have more to deal with hyper-growth that would come from GMO foods and Agent Orange and other such environmental aggressors. Before AO was discovered as a defoliant at mega-doses, it was planned to super-grow soy. I suspect that these various poisons combined with mercury and other such poisons are gnarling their brains like root-bound plants. I have made two boys with varying degrees of the diagnosis.

The real reason is that although there are very real cases of autism... Lately the culture has been to misdiagnose the crap out of children , whether its ADHD or Aspergers or autism the majority of diagnosis are wrong boys act out more so they are misdiagnosed more often.

Boys seem to be at higher risk for dyslexia, too, and hemophilia, among other problems. Perhaps the question might to be asked, "Are these problems in any way sex-linked?"

In domestic cats, a cat showing coat color with three colors can safely be assumed to be female, because there is a sex-linked lethal gene which almost always prevents a male cat being born with such coloration. Perhaps there are some other sex-linked problems which are not lethal, merely problematic.